JPH05328161A - Horizontal centering circuit - Google Patents

Abstract

PURPOSE:To obtain the horizontal centering circuit capable of making a centering current variable with low-voltage change and facilitating the control by a micro computer, etc., and advantageous in terms of structure and cost. CONSTITUTION:A base level portion of a pulse V3 produced at a tap (d) of a flyback transformer 13 is rectified by a rectifier diode 15, a DC voltage E3 is generated in a smoothing capacitor 16 and a DC current is supplied to a horizontal deflection coil 2 through a resistor 17. On the other hand, a collector current Ic1 of a pnp transistor(TR) 18 flows through a horizontal deflection coil 2 in a reverse direction to a current by the DC voltage E3. Since the collector current Ic1 is controlled by the voltage Ect, the DC current flowing to the horizontal deflection coil 2 is controlled resultingly and horizontal centering control is implemented. The voltage Ect is low and the control by a microcomputer or the like is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal centering circuit for moving a raster position on a picture tube right and left by superimposing a direct current having an arbitrary direction and magnitude on a horizontal deflection coil in a television device or the like. Regarding

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing an example of a conventional horizontal centering circuit. In FIG. 6, reference numeral 1 denotes a horizontal output circuit that causes a sawtooth wave current Iy to flow in the horizontal deflection coil 2 by performing a switching operation of a horizontal deflection cycle.
Further, 3 is a linearity coil connected to this horizontal deflection coil, and 4 is an S-shaped correction capacitor. When the sawtooth wave current Iy flows through the horizontal deflection coil 2, a pulse Vc having a half cycle of a sine wave having a horizontal deflection period is generated at one end thereof. This pulse Vc is applied to one end of the primary winding 5a of the flyback transformer 5. A DC power supply voltage Eb is applied to the tap b near the other end of the primary winding 5a,
As a result, the DC output current of the horizontal output circuit 1 is supplied.

Further, the pulse Vc applied to the primary winding 5a is boosted by the secondary winding 5b to become a high voltage pulse Vhv. Then, this Vhv is rectified by the high voltage rectifier diode 6 to obtain a direct current high voltage HV and is guided to the anode of a picture tube not shown. The other end of the secondary winding 5b is grounded or connected to a brightness limiting circuit (ABL). Primary winding 5
Another tap a of a and a tap b connected to the DC power supply Eb
A positive pulse V1 in which the pulse Vc is stepped down is generated between the first pulse Vc and the positive pulse V1.
Then, the base portion of the first smoothing capacitor 9 is rectified, and a DC voltage E1 in the direction shown is generated across the first smoothing capacitor 9. Then, similarly, a negative pulse V2 is generated between the one end c of the primary winding 5a and the tap b, and this is rectified at the base portion by the second rectifying diode 8 and the second smoothing capacitor 10
A DC voltage E2 is generated at the two ends in the direction shown in the figure.

A potentiometer 11 is connected to both ends of the potentiometer 11 such that the sum of the voltages E1 and E2 is applied. At the same time, the movable piece q of the potentiometer 11 is the choke coil 12
After that, it is guided to the connection point between the linearity coil 3 and the S-shaped correction capacitor 4 described above. In this FIG.
When the movable piece q of the potentiometer 11 moves to the p side, the voltage E1 is mainly inserted in the loop of the horizontal deflection coil 2, the primary winding 5a of the flyback transformer, and the choke coil 12, and therefore, A direct current Ict1 for centering indicated by a solid arrow in the figure flows. On the contrary, when the movable piece q moves to the r side of the potentiometer 11, the voltage E2 enters the above loop, and the reverse current Ict2 flows this time.

In this way, by moving the movable piece q of the potentiometer 11 from p to r, the current flowing in the direction of Ict1 gradually decreases its value, and after passing through zero, I
It changes continuously in the direction of ct2 until it becomes maximum. This DC voltage is the sawtooth wave current I of the horizontal deflection coil 2 as it is.
Since it flows superimposed on y, the direct current level of the sawtooth wave Iy is shifted by the movement of the potentiometer 11, and so-called centering adjustment is achieved, which moves the raster position on the picture tube to the left and right. At this time, the parabolic voltage Vpb is generated in the S-shaped correction capacitor 4,
Since this is blocked by the choke coil 12, it does not affect the action of the centering described above.

[0006]

The conventional basic horizontal centering circuit shown in FIG. 6 has some problems. First, the potentiometer 11 used here
Since a relatively large current must be passed, a large wire wound type must be used, which is one of the design problems in terms of cost and space. Further, there is a problem that the potential of the potentiometer 11 with respect to the ground point is a high value which is almost close to the power supply voltage Eb. That is, in a display monitor or the like, there is a case where it is desired to perform this horizontal centering adjustment by an external adjuster unit. However, at this time, if the potentiometer 11 is at a high voltage with respect to the ground, it is safe. It was difficult to pull out the lead.

Also in general television receivers, in recent years, adjustment of each part is often controlled and controlled by microcomputer output. Even in this case,
It is difficult to directly control a potentiometer circuit having a high potential with respect to the ground with such a large current with a voltage value obtained by D-A converting the output of the microcomputer. In the examples of conventional microcomputer-controlled television receivers, , It was usual to exclude the horizontal centering of this raster from the control target and substitute it for the phase adjustment of the image. However, with this method, it is impossible to correct the screen loss phenomenon at either the left or right side when the center of the raster is largely deviated, and the raster overscan amount is unavoidably increased to prevent the screen loss. This has been a problem in that the proportion of the image information that is not displayed increases. Further, the circuit of FIG. 6 requires two taps a and b on the primary winding 5a of the flyback transformer 5, but this is also disadvantageous in terms of space and cost, so the number is reduced. Is desirable.

[0008]

In order to solve the above-mentioned problems of the prior art, the present invention provides (1) a sawtooth saw in a series circuit of a horizontal deflection coil and an S-shaped correction capacitor by a switching operation of a horizontal deflection cycle. A horizontal output circuit for flowing a wave current, a flyback transformer having one end connected to one end on the hot side of the horizontal deflection coil and the other end connected to a DC power supply voltage, or a primary winding of the horizontal output transformer,
A series circuit of a choke coil and a constant current circuit connected between the DC power supply voltage, the horizontal deflection coil and the S-shaped correction capacitor, and one end of the output connected to the DC power supply voltage One end of the DC voltage generating circuit for generating a DC voltage in the direction opposite to the DC power supply voltage, the other end of the output of the DC voltage generating circuit, the choke coil and the constant current circuit connection Provided with a resistor connected between the point and, to provide a horizontal centering circuit characterized by changing the constant current value of the constant current circuit, (2) by the switching operation of the horizontal deflection cycle, A horizontal output circuit for flowing a sawtooth wave current in a series circuit of a horizontal deflection coil and an S-shaped correction capacitor, one end of which is connected to one end of the horizontal deflection coil on the hot side, and the other end of which is connected to a DC power supply voltage. The primary winding of the flyback transformer or the horizontal output transformer, the DC power supply voltage, the choke coil and the first constant current circuit connected between the horizontal deflection coil and the S-shaped correction capacitor. A series circuit and one end of the output is connected to the DC power supply voltage,
The other end of the output is a DC voltage generating circuit that generates a DC voltage in the direction opposite to that of the DC power supply voltage, the other end of the output of the DC voltage generating circuit, the choke coil and a constant current circuit. Second connected between the connection point and
And a constant current circuit for changing the constant current value of the first constant current circuit or the constant current value of the second constant current circuit. 3. The horizontal centering circuit according to claim 2, wherein (3) the constant current value of the first constant current circuit and the constant current value of the second constant current circuit are differentially changed. I will provide a.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A horizontal centering circuit of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. Here, the horizontal output circuit 1,
The horizontal deflection coil 2, the linearity coil 3, the S-shaped correction capacitor 4, the high-voltage rectification diode 6, and the choke coil 12 operate according to the same principle as that of the conventional example shown in FIG.

The flyback transformer 13 is slightly different from the flyback transformer 5 shown in FIG. 6, and has a primary winding 13a.
The top tap has only one of d. Further, a current adjusting resistor 14 is added between the hot side winding end of the primary winding 13a and the horizontal output circuit 1 and the horizontal deflection coil 2. A rectifying diode 15 is connected to the tap d, and rectifies the base of the pulse V3 generated at the tap d,
The smoothing capacitor 16 (DC voltage generating circuit) connected between the rectifying diode 15 (DC voltage generating circuit) and the power supply voltage Eb generates the DC voltage E3 in the direction shown in the figure. Further, a resistor 17 is connected between the smoothing capacitor 16 and one end of the choke coil 12, and a direct current is passed therethrough.

The collector-emitter terminal of the pnp transistor 18 is connected between the connection point of the choke coil 12 and the resistor 17 and the power supply voltage Eb. The base terminal of the pnp transistor 18 is connected to the collector terminal of the npn transistor 20 via the base resistance 19, and the emitter terminal thereof is grounded by the emitter resistance 21.
The base terminal of the npn transistor 20 is connected to the output terminal of the operational amplifier 23 via the base resistor 22. The inverting input terminal of the operational amplifier 23 is connected to the emitter terminal of the npn transistor 20, and the control voltage Ect from the outside is applied to the non-inverting input terminal.

In this way, the circuit composed of the elements from the pnp transistor 18 to the operational amplifier 23 in FIG. 1 has the pnp transistor 18 according to the value of the voltage Ect.
Will function as a constant current circuit (first constant current circuit) 24 for keeping the value of the current flowing from the emitter to the collector constant. That is, the pnp transistor 18 flowing through the resistor 19
Is a collector current of the npn transistor 20 and is substantially equal to its emitter current Ie2.
Then, the base current Ib2 of the npn transistor 20 is controlled by the output of the operational amplifier 23 so that the voltage generated across the resistor 21 by the emitter current Ie2 always matches the voltage Ect, and as a result, the emitter current Ie2 is controlled.
Then, the base current Ib1 of the pnp transistor 18 is made constant according to the value of the voltage Ect. The collector current Ic1 of the pnp transistor 18 is almost independent of other conditions,
Since it flows at a value of hFE times the base current Ib1, this means that the circuit is a constant current circuit that can be freely controlled by the value of the voltage Ect.

Next, how the centering current flowing through the deflection coil 2 changes when the collector current Ic1 of the pnp transistor 18, that is, the value of the constant current, is changed by the voltage Ect will be described. First, FIG. 2 shows a case where the voltage Ect is set to zero. At this time, as is clear from the above description, p
Since the base current Ib1 of the np transistor 18 becomes zero, its collector current Ic1 also does not flow. Therefore, originally p
The point between point e and point where the collector and emitter of the np transistor 18 are connected is equivalent to disconnection. Then, in the loop formed by the primary winding 13a, the resistor 14, the horizontal deflection coil 2, the linearity coil 3, the choke coil 12 and the resistor 17 of FIG.
Is equivalent to the inserted form. Therefore, the direct current component Ict1 flowing in the horizontal deflection coil 2 flows through the path shown by the loop of the arrow in FIG. 2, and this acts as a horizontal centering current to move the horizontal position of the image.

Next, the operation when the control voltage Ect in FIG. 1 becomes maximum will be described with reference to FIG. In this case, npn
The base current Ib2 of the transistor 20 and the base current Ib1 of the pnp transistor 18 become maximum, and the pnp transistor 18 becomes saturated. Therefore, the collector-emitter, that is, the two points e and f is equivalent to a short circuit. In FIG. 1, a DC current of Ih flows from the DC power source Eb as a current consumption of the horizontal output circuit 1. FIG. 3 shows how the route e and f reach the horizontal output circuit 1 when a short circuit occurs.

That is, this current Ih passes through the primary winding 13a of the flyback transformer 13 and the current adjusting resistor 14, and the component of It flowing into the horizontal output circuit 1, the choke coil 12, the linearity coil 3 and the horizontal deflection coil 2 Then, it is divided into two components of Ict2 which also flows into the horizontal output circuit 1. And this horizontal deflection coil 2
The Ict2 shunting to the side performs the horizontal centering operation, and its direction is opposite to that of Ict1 in FIG. The value of the current Ict2 is maximized when e and f are short-circuited, that is, when the pnp transistor 18 in FIG. 1 is saturated. Then, the control voltage Ect decreases and the base current Ib1 decreases, so that it gradually decreases to that value, and finally becomes zero. Further, when the value of the control voltage Ect is reduced, the component of the current Ict1 shown in FIG.
The direction of the current flowing in the horizontal deflection coil 2 is reversed, and Ect becomes zero, so that the current value of Ict1 becomes maximum as described above.

As is clear from the above description, the control voltage E
Depending on the value of ct, the value of the direct current flowing through the horizontal deflection coil 2 can be adjusted freely in either the positive or negative direction around zero, and as a result, horizontal position of the image can be finely moved as horizontal centering. become. Moreover,
Since Ect at the time of this adjustment has a low voltage with respect to the ground and does not require electric power, it can be easily controlled by an external device or driven by a microcomputer or the like. The current adjusting resistor 14 is not particularly indispensable. This is because even if the pnp transistor 18 is completely saturated, if the current Ict2 is still insufficient, the resistance 14
The purpose is to reduce the current It side and increase Ict2. The shunt ratio between the currents Ict2 and It is proportionally divided (divided according to the ratio) by the value of the DC resistance of both paths. If the DC resistance values of the primary winding 13a of the flyback transformer, the choke coil 12, the horizontal deflection coil 2, etc. are set to values that allow a sufficient amount of Ict2 to flow, the current adjusting resistor 14 becomes unnecessary.

In FIG. 1 according to one embodiment of the present invention, a high voltage HV is introduced from the secondary winding 13 of the flyback transformer through the diode 6. However, in this case, it is desirable that the change in the high voltage current Ia is as small as possible. This is because the DC consumption current Ih of the horizontal output circuit 1 changes according to the change of Ia, and the current Ict2 in FIG. 3 changes, which affects the centering amount. Therefore, this FIG. 1 is applied only to a small-sized receiver or a monochrome receiver in which the amount of change in the high-voltage current Ia is small. If this circuit is applied to a normal color image receiver, 13 is operated as a horizontal output transformer instead of a flyback transformer which supplies high voltage, and the high voltage applied to the cathode of the picture tube is different from that of this circuit. It must be a deflection high voltage separation type circuit supplied from the part.

FIG. 4 shows another circuit example of the present invention, which is constructed so that the centering current is not affected by the change in the high voltage current Ia. Here, since the numbers 1 to 24 have almost the same functions as those of the same numbers in FIGS. 6 and 1 to 3, the detailed description thereof will be omitted. This FIG. 4 is different from FIG. 1 in that the resistor 17 of FIG. 1 is replaced between the collector and the emitter of the second pnp transistor 25. And the second pnp
The base terminal of the transistor 25 is grounded via the base resistor 26. In this case, the emitter potential of the second pnp transistor 25 slightly changes depending on the value of the current Ih and the value of Ict2, but the amount of change is slight and almost constant as compared with the value of the voltage Eb. Therefore, it can be considered that the base potential is almost constant, and therefore the base current Ib3 flowing through the base resistor 26 is also constant. Therefore, naturally, the collector current Ic3 of the second pnp transistor 25 also becomes constant, and in FIG. 4, the resistor 17 of FIG. 1 is replaced with the second constant current circuit using the second pnp transistor and the base resistor 26. become.

In the case of FIG. 1, the pnp transistor 18 also forms a constant current circuit (first constant current circuit), but in such a configuration, the potential at point e changes slightly when the current Ih actually changes. However, since this is a value that cannot be ignored with respect to the voltage E3 having a relatively small value, the value of the current flowing through the resistor 17 also changes due to the influence. As a result, even if the current flowing through the pnp transistor 18 is constant, the centering current flowing through the horizontal deflection coil 2 through the choke coil 12 also changes depending on the value of the current Ih or the high voltage current Ia. Therefore, as shown in FIG. 4, the portion which was the resistor 17 in FIG. 1 is also the second constant current circuit including the second pnp transistor 25. By doing so, the current flowing through this portion is constant. Therefore, even if the current Ih or the high voltage current Ia changes, the value of the centering current flowing through the horizontal deflection coil 2 does not change. Therefore, there is no problem in using the circuit of FIG. 4 in a large-sized television receiver in which the value of the high voltage current Ia changes greatly depending on the brightness of the picture tube.

In FIG. 4, the base current Ib3 of the transistor 25 is kept constant and the base current of the transistor 18 is changed, but this relationship may be reversed. For example, if one end of the resistor 26 is connected to the collector of the transistor 20 instead of being grounded and conversely one end of the resistor 19 is grounded instead of the collector of the transistor 20, the base current Ib1 becomes constant and conversely the base current Ib3 becomes variable. However, the centering current flowing in the horizontal deflection coil 2 can be continuously changed. Note that, as the constant current circuit, a system in which the base current of the transistor is made constant is taken as an example up to now.
Of course, other constant current circuits known in the art may be used.

FIG. 5 shows another embodiment according to the present invention. Note that, in FIG. 5, the description of the components having the same numbers as those in FIG. 6, FIG. 1, and FIG. In FIG. 5, npn transistors 27 and 28 whose emitters are commonly connected are provided in place of the control npn transistor 20. And each collector has pn
From the bases of p-transistors 18 and 25 to resistors 19 and 26
Are connected. Further, a resistor 29 is provided between the common emitter of these two npn transistors 27 and 28 and the ground.
Are connected. Further, here, one n represented by 27
The base of the pn transistor is connected to the DC power supply E and the base resistors 30 and 31 from the ground. The other npn transistor 28 is connected to the base of the resistor 32, the potentiometer 33 and the resistor 34 which are also connected between the power source E and the ground. Is connected to the movable piece of the voltage divider.

In this way, for example, the potentiometer 3
3, the base current of the npn transistor 28 is increased, and the collector current of the transistor 28 flowing through the resistor 19, that is, the base current of the pnp transistor 18 is increased. Then, conversely, the collector current of the npn transistor 27, that is, pnp
The base current of transistor 25 decreases, which in turn decreases the collector current of transistor 25. On the contrary, if the potentiometer 33 is moved to decrease the collector current flowing through the pnp transistor 18 contrary to the previous case, the collector current of the one pnp transistor 25 increases this time.

As described above, in the circuit of FIG. 5, the collector current of the pnp transistor 18 for causing the centering current in the deflection coil to flow upward from the bottom of the drawing, and the centering current described above flow in reverse from top to bottom. Pn for
The increase and decrease of the collector current of the p-transistor 25 work in opposition to each other.
The rate of change of the centering current is larger than that of FIG. 4 in which only the operation state of 8 changes. The collector currents of these two pnp transistors 18 and 25 depend on the temperature characteristics of the respective current amplification factors hfe. However, regarding the centering current, both collector currents cancel each other, so that the influence due to the change in ambient temperature is not affected. Few.
However, as illustrated in the description of FIGS. 2 and 3, one pn
If the p-transistor is cut off or becomes saturated, the temperature change of the other remaining transistor cannot be canceled, and the value of the centering current greatly changes due to the change of ambient temperature.

In FIG. 5, since the increase and decrease of the collector currents of both pnp transistors work in a complementary manner, the change rate of the centering current is about twice as large as that in FIG. Since a sufficient centering current can be obtained even if the state is not reached, the influence of temperature is small for the reason described above.

[0025]

As described in detail above, the horizontal centering circuit of the present invention changes the low voltage with respect to the ground so that the centering current that can be continuously changed in both positive and negative directions with respect to zero becomes horizontal. Since it can be supplied to the deflection coil and is easily controlled by an external control or a microcomputer, the image position of the television receiver can be accurately adjusted. Further, the flyback transformer required for this centering needs to be changed by adding one tap, and an expensive and large winding potentiometer is not necessary, which is structurally and cost-effective. Further, according to the present invention, it is possible to provide a centering circuit that is not affected by the change in the brightness of the image on the picture tube and is hardly affected by the change in the ambient temperature.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a horizontal centering circuit of the present invention.

FIG. 2 is a diagram for explaining the operation of the first embodiment.

FIG. 3 is a diagram for explaining the operation of the first embodiment.

FIG. 4 is a circuit diagram showing a second embodiment of the horizontal centering circuit of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the horizontal centering circuit of the present invention.

FIG. 6 is a diagram showing an example of a conventional horizontal centering circuit.

[Explanation of symbols]

 1 horizontal output circuit 2 horizontal deflection coil 3 linearity coil 4 S-shaped correction capacitor 5 flyback transformer 6 high-voltage rectifier diode 11 potentiometer 12 choke coil 13 flyback transformer 15 rectifier diode (DC voltage generation circuit) 16 smoothing capacitor (DC voltage generation) Circuit 17 resistance 18 pnp transistor 20 npn transistor 23 operational amplifier 24 constant current circuit (first constant current circuit) 25 second pnp transistor (second constant current circuit) 27 npn transistor 28 npn transistor

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[Procedure amendment]

[Submission date] April 1, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

In order to solve the above-mentioned problems of the prior art, the present invention (1) saws a series circuit of a horizontal deflection coil and an S-shaped correction capacitor by a switching operation of a horizontal deflection cycle. A horizontal output circuit for passing a wave current, a flyback transformer having one end connected to one end of the horizontal deflection coil on the hot side and the other end connected to a DC power supply voltage, or a primary winding of the horizontal output transformer, A DC power supply voltage, a series circuit of a choke coil and a constant current circuit connected between the horizontal deflection coil and the S-shaped correction capacitor, and one end of the output connected to the DC power supply voltage One end has a DC voltage generating circuit for generating a DC voltage that is applied in a direction opposite to the DC power supply voltage, the other end of the output of the DC voltage generating circuit, and the choke coil. And a resistor connected between a connection point with the constant current circuit and a constant current value of the constant current circuit is changed, and a horizontal centering circuit is provided. (2) Horizontal A horizontal output circuit that causes a sawtooth wave current to flow in a series circuit of a horizontal deflection coil and an S-shaped correction capacitor by switching operation of the deflection cycle, and one end is connected to one end on the hot side of the horizontal deflection coil, and the other end is DC A flyback transformer or a primary winding of a horizontal output transformer connected to a power supply voltage, the DC power supply voltage, a choke coil and a first constant coil connected between the horizontal deflection coil and the S-shaped correction capacitor. A series circuit with a current circuit and one end of the output are connected to the DC power supply voltage, and the other end of the output generates a DC voltage in a direction to be applied in a direction opposite to the DC power supply voltage. A first constant current circuit connected between the choke coil and the constant current circuit; and a second constant current circuit connected between the choke coil and the constant current circuit. Provided is a horizontal centering circuit, characterized in that either the constant current value of the constant current circuit or the constant current value of the second constant current circuit is changed. (3) The first constant current The constant current value of the circuit and the constant current value of the second constant current circuit,
A horizontal centering circuit according to (2) is characterized in that it is changed differentially.

Claims (3)

[Claims] 1. A horizontal deflection cycle switching operation,
A horizontal output circuit that causes a sawtooth wave current to flow in a series circuit of a horizontal deflection coil and an S-shaped correction capacitor, and a fly with one end connected to the hot end of the horizontal deflection coil and the other end connected to a DC power supply voltage. A primary winding of a back transformer or a horizontal output transformer; the DC power supply voltage; and a series circuit of a choke coil and a constant current circuit connected between the horizontal deflection coil and an S-shaped correction capacitor; One end of the output is connected to the power supply voltage, and the other end of the output is a DC voltage generating circuit that generates a DC voltage in a direction that is applied in a direction opposite to the DC power supply voltage, and another output of the DC voltage generating circuit. It has one end and a resistor connected between a connection point of the choke coil and the constant current circuit, and is configured to change the constant current value of the constant current circuit. Flat centering circuit. 2. A horizontal deflection cycle switching operation,
A horizontal output circuit that causes a sawtooth wave current to flow in a series circuit of a horizontal deflection coil and an S-shaped correction capacitor, and a fly with one end connected to the hot end of the horizontal deflection coil and the other end connected to a DC power supply voltage. A primary winding of a back transformer or a horizontal output transformer; a series circuit of a choke coil and a first constant current circuit connected between the DC power supply voltage and the horizontal deflection coil and the S-shaped correction capacitor; An output of the DC voltage generating circuit, one end of the output of which is connected to the DC power supply voltage, and the other end of the output of which generates a DC voltage in a direction that is applied in a direction opposite to the DC power supply voltage. A second constant current circuit connected between the other end of the first constant current circuit and a connection point between the choke coil and the constant current circuit, and a constant current value of the first constant current circuit or the second constant current circuit. Horizontal centering circuit which is characterized in that so as to vary either the constant current value of the constant current circuit. 3. The horizontal centering circuit according to claim 2, wherein the constant current value of the first constant current circuit and the constant current value of the second constant current circuit are differentially changed. ..